14 METHODS OF ANALYSIS [Chap. 



flame, below a red heat, until all volatile matter is driven off. Digest the residue 

 with hot water, filter through a small filter and dilute the filtrate, if necessary, so 

 that for each decigram of potassium oxid there will be at least 20 cc. of liquid. Acid- 

 ify with a few drops of hydrochloric acid and add platinum solution in excess. Evap- 

 orate on a water bath to a thick paste and treat the residue with 80% alcohol, both by 

 decantation and after collecting on a Gooch or other form of filter, dry for 30 minutes 

 at 100°C. and weigh. If there is an appearance of foreign matter in the double salt, 

 it should be washed as in 42 (a) with several portions of 10 cc. each of the 

 ammonium chlorid solution. 



THOMAS OR BASIC SLAG.— TENTATIVE. 



46 MECHANICAL ANALYSIS. 

 Proceed as directed under 1, using 10 grams of material. 



47 PREPARATION OF SAMPLE. 

 Prepare the sample as directed under 2. 



TOTAL PHOSPHORIC ACID. 

 Gravimetric Method. 



48 PREPARATION OF SOLUTION. 



Prepare the solution for analysis as directed under 5 (C), or in strong hydrochloric 

 acid alone. In the latter case after the portion for analysis is measured out, add 

 nitric acid and heat for a few minutes. 



49 DETERMINATION. 



Dehydrate an aliquot (20 cc.) of 48 by evaporating to dryness on a steam or hot 

 water bath; treat with 5 cc. of hydrochloric acid and 25 cc. of hot water; digest in 

 order to complete solution and filter off silica. From this point proceed as directed 

 under 6. Before precipitating with magnesia mixture, add 5 cc. of 5% sodium acetate. 



50 Volumetric Method. 



Prepare the solution as directed under 5 (C) and determine the phosphoric acid 

 in an aliquot of this solution as directed under 9, standardizing the solutions 

 against a standard phosphate material of approximately the same composition 

 as the sample under examination. 



CITRATE-SOLUBLE PHOSPHORIC ACID. 



Gravimetric Method. — {Wagner's Method.) 



51 PREPARATION OF SOLUTION. 



Weigh 5 grams of the slag into a 500 cc. Wagner flask containing 5 cc. of 95% 

 alcohol. (The flask should have a neck width of at least 22 mm. and should be 

 marked at least S cm. below the mouth.) Make up to the mark with 2% citric acid 

 solution of a temperature of 17.5°C. Fit the flask with a rubber stopper and place 

 at once in a rotary apparatus, shaking the flask for 30 minutes at the rate of 30-40 

 revolutions per minute, at the end of which time remove the flask, filter immediately 

 on a dry filter and analyze the solution at once. 



